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11
…
Muhammad Abed
Osama Al-khader
Muhammad khatatbeh
1 | P a g e
-Some points from the previous lecture: -
In the previous lecture, we have seen how we can get excitatory post synaptic
potentials (EPSP) and inhibitory post synaptic potentials (IPSP), also the types of
summation which are spatial summation and temporal summation.
-The action potential generates in the axon hillock.
2 | P a g e
“The new lecture”
Two notes to know: -
*when we have many presynaptic neurons synapsing with one neuron, we call this
synaptic organization as convergence. Results in many inputs from presynaptic neurons
received by single postsynaptic neuron.
*when we have one neuron with its many terminals synapsing with many neurons, we
call this synaptic organization as divergence. It results in converting the signal from one
neuron to many postsynaptic neurons.
In our nervous system, we have many divergence and convergence between our neural
network structures.
3 | P a g e
Compound action potential: -
It is a recording for action potential with multiple peaks or waves.
We can do it by performing a stimulus to the skin which will stimulate all
neurons of a nerve, then we put a sensor away from the stimulus.
Each wave reflects the activity of a group of fibers with a similar conduction
velocity. So, we have many waves because of the difference in the velocity of
conduction of the action potential due to the difference in the type of the
neuron and the diameter of it.
This reading helps us to check whether the neurons of a person of a nerve is
working properly or not.
More details with Dr. Faisal. We don’t have to know much right now.
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Autonomic nervous system (ANS) The autonomic nervous system is the portion of the nervous system that
controls most visceral functions of the body. This system helps to control
arterial pressure, gastrointestinal motility, gastrointestinal secretion, urinary
bladder emptying, sweating, body temperature, and many other activities,
some of which are controlled almost entirely and some only partially by the
autonomic nervous system.
4 | P a g e
The general function of it is the Control and Adaptation of body systems to
internal and/or external changes. These changes include fear, stress, eating,
digesting, etc.
The system is divided into two subdivisions sympathetic and parasympathetic.
-Physiological characteristics of ANS: -
*speed of onset: ANS can produce dramatic changes in the level of activity of
organs they innervate within seconds.
*Autonomic nature: functions and the regulation by this system occurs
without conscious control as the name indicates.
*Tonic activity (of each division): means certain level of activity over the body.
As example, sometimes the level of activity of the sympathetic nervous
systems increases and the level of activity of the parasympathetic nervous
system decreases. So, this system is continually active. The value of this
5 | P a g e
feature is that it allows a single nervous system both to increase and decrease
the activity of a stimulated organ. For instance, sympathetic tone normally
keeps almost all the systemic arterioles constricted to about one-half their
maximum diameter. By increasing the degree of sympathetic stimulation
above normal, these vessels can be constricted even more; conversely, by
decreasing the stimulation below normal, the arterioles can be dilated.
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Examples on some situations when the system works:
When your eye is exposed to intense light your pupil constricts, an in the low
light situation your eye pupil dilates.
Constriction of the pupil is known as miosis, while the dilation of the pupil is
known as mydriasis.
Temperature: in warm environment, cutaneous vasodilation and sweating
occurs, and vasoconstriction in cold.
vaso-vessel
Stress (mainly for sympathetic nervous system and adrenal medulla): as in
fight or flight situation many responses happen. As an increase in the heart
rate tachycardia, widely dilated pupils, pallor (pale of fear due to low blood
flow to skin), goose pimples (hair standing over skin), cold sweat(because of
the low blood flow to the sweat so it won’t be heated) and dry mouth (low
activity of salivary gland because it is not the perfect time to digest food)
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Sympathetic and parasympathetic nervous systems (general overview)
sympathetic nervous system- SNS
parasympathetic nervous system- PNS
there are 3 differences and 1 similarity between them.
The similarity is that the two types have two neurons starting from the place
of origin to the effector organ, this pathway from the origin to the effector
organ is called the Axe. The Axe in both types consists of two neurons. (There
is an exception in SNS will be noticed later).
Differences: The origin: the sympathetic nervous system originates from the spinal cord
from the thoracolumbar region (from T1 to L2) *In the handout to L3. The
6 | P a g e
parasympathetic nervous system originates from the sacral region (the lower
most region of the spinal cord S2, S3) and from certain nuclei in the cranial
region, so the parasympathetic nervous system has a craniosacral origin.
Note: - in the handout, the origin for the PNS is S3, S4 (sometimes S2 and S5)
in the book, S2, S3.
the most important is to know that it is craniosacral.
The second difference is the function and the level of activity in certain
situations. For example, SNS mainly active during “fight or flight” situations
which involves stress and fear … , while PNS is specialized in “rest and digest”.
The third difference is the length of the first and the second neuron as we said
in the similarity between PNS and SNS. In the SNS, the first neuron is short
very near to the spinal cord and the second neuron is long. The opposite in the
PNS where the first neuron extends from its origin to a very close position near
the effector organ or in it, where it synapses with the second short neuron.
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Sympathetic nervous system in more details
Physiological anatomy: Two neurons carry impulses of the SNS from CNS to the
effector organ. The first is known as preganglionic (before the ganglion) neuron
and the second is known as the postganglionic neuron (after ganglion).
The ganglion: a cluster of cell bodies.
For the SNS there are three possibilities for the synapsing condition.
*Look at the picture below.
The two neurons may meet in the paravertebral ganglia, the paravertebral
ganglia are closer to the spinal cord than prevertebral ganglia.
(Ganglia is the plural for ganglion).
7 | P a g e
The two neurons will pass from the paravertebral ganglia without synapsing then
meeting in the prevertebral ganglia (located in the abdomen).
note: the prevertebral ganglia are free ganglia that are not connected to each
other, unlike the paravertebral ganglia. Also, they are three in number, celiac
ganglion, superior and inferior mesenteric ganglia.
The third case which is the exception mentioned in the beginning of the sheet. In
this case, there is no two neurons only one neuron passing from the spinal cord
to the adrenal gland where they synapse with cells called chromaffin cells results
in releasing epinephrine (adrenaline) in the blood stream.
Note1- in the SNS we have a lot of divergence and convergence to do the
diffuse reaction which is a
characteristic of SNS. While in PNS,
almost no convergence and
divergence.
Note2- in the first situation
where two neurons meet in the
paravertebral ganglia, the first
neuron (the preganglionic neuron)
might synapse with the second
neuron at the same, lower or
above segmental level; i.e. some
terminals of some preganglionic
neurons synapse at a higher
segmental level, lower segmental
level or above the segmental level. ----------------------------------------------
Effects of sympathetic stimulation
(Fight or Flight)
SNS innervates widely distributed
tissues including sweat glands,
smooth muscles of blood vessels
supplying skeletal muscles, skin,
8 | P a g e
etc. and smooth muscle cells of hair follicles. All of these target tissues don’t have
any parasympathetic innervation. So, the effects are:
Controlling blood pressure. As an example, by changing the diameter of the
blood vessels.
Body temperature by effecting cutaneous blood vessels and sweat glands.
Handling stress (fight or flight reaction)
the main goal is to promote the production of energy for muscular work and to
shut down organs with nonessential function. (You don’t need to digest food
while facing a lion). Effects include: -
*cardiovascular system: by redistributing blood to skeletal muscles and reducing
blood flow for skin and mesentery. Also, increasing the heart rate and the force
of contraction.
*Respiratory system: by relaxation of bronchial muscle which results in
bronchodilation (increasing in the diameter of bronchi) to get more oxygen.
*Digestive system: inhibition of motility and secretion. (Results in dry mouth due
to low salivation.
*Metabolic effects: increase in the rate of mobilizing glucose and lipids because
we need nutrients for the muscles.
Glucose is stored in the form of glycogen in our bodies.
If it was easy, everyone would do
it, but it is the hardness that makes
it great.